Organopolysiloxane compounds having aliphatic unsaturated monovalent hydrocarbon groups on silicon atoms are useful as the base polymer in addition-curable silicone compositions. Because addition-curable silicone compositions cure to form silicone gels and silicone rubbers having excellent electrical properties, cold resistance and the like, they are widely used as, for example, encapsulants, fillers and coatings for electrical and electronic components and for semiconductor devices, and as photosemiconductor insulating/covering/protecting agents.
Addition-curable silicone compositions use, for the most part, an organopolysiloxane compound having vinyl groups on silicon atoms as the base polymer, which compound undergoes a hydrosilylation reaction with organohydrogen(poly)siloxane to give a silicone cured product.
However, aliphatic unsaturated hydrocarbon groups capable of being used in hydrosilylation reactions are not inherently limited to vinyl groups; so long as an organopolysiloxane compound has, as a partial structure, aliphatic carbon-carbon multiple bonds, use of the compound as the base resin of an addition-curable silicone composition is theoretically possible.
In particular, when a base polymer having, as a partial structure, at least one unit of general formula (b) below
(wherein R1 is a hydrogen atom or a monovalent hydrogen group of 1 to 20 carbon atoms which may have a substituent, each R1 being the same or different; and R4 is a monovalent hydrocarbon group of 1 to 20 carbon atoms which may have a substituent, each R4 being the same or different) is used, improved control of the curing reaction rate and improved composition properties due to the substituent effects by the triorganosilyl groups substituted onto vinyl groups are expected.
The simplest compounds having, as partial structures, two units of general formula (b) are represented by general formula (c) below
(wherein R1 is a hydrogen atom or a monovalent hydrogen group of 1 to 20 carbon atoms which may have a substituent, each R1 being the same or different; and R4 is a monovalent hydrocarbon group of 1 to 20 carbon atoms which may have a substituent, each R4 being the same or different).
A compound that corresponds to general formula (c) appears in a synthesis example for 1,1,3,3-tetramethyl-1,3-bis[2-(trimethylsilyl)ethenyl]-(E,E)-disiloxane of formula (6) below that has been reported in the literature (Org. Biomol. Chem. 9, 504 (2011); Non-Patent Document 1).

However, this compound has a small molecular weight and has been difficult to use as the base polymer of addition-curable silicone compositions.
Here, because addition-curable silicone compositions cure to form silicone gels, silicone rubbers and hardcoats having excellent electrical properties, cold resistance, heat resistance and chemical stability, they are widely used as, for example, encapsulants, fillers and coatings for electrical and electronic components and for semiconductor devices, and as photosemiconductor insulating/covering/protecting agents. Moreover, by including various types of inorganic fillers, it is possible to increase the strength of the composition and to impart heat resistance. In addition, such compositions are also used as heat-dissipating materials and electrically conductive materials for electronic components such as semiconductor devices and LED substrates.
Although the properties desired of these addition-curable silicone compositions appear to differ somewhat depending on the technical field and application, a good shelf stability and a good heat resistance are among the most important properties in any technical field and application.
Among the methods that have been disclosed for increasing the shelf stability of compositions are methods wherein a hydrosilylation catalyst that promotes an addition reaction is included within the composition by being embedded and encapsulated in a thermoplastic resin or silicone resin having a specific melting point, and is subsequently released into the silicone composition by melting the resin under applied heat or by dissolving the resin with a solvent (Patent Documents 1 to 6: JP-A S58-37053, JP-A S64-51140, JP-A H02-9448, JP-A H02-14244, JP-A H05-202193 and JP-A H07-196921). However, a drawback of such methods involving microcapsulation is that a high-concentration platinum family metal catalyst is unevenly distributed within the composition, which tends to give rise to localized curing.
A method that uses an acetylene alcohol or the like as a reaction inhibitor has also been proposed, and is described as preventing partial curing reactions (Patent Document 7: JP-A H04-46962). Yet, this composition too, when used more broadly in various applications, sometimes gives rise to a number of drawbacks. For example, in cases where a foam is to be obtained on a heating line by including a hydroxyl group source such as an alcohol or water in the composition, it is known that foaming due to a small amount of dehydrogenation at the start of the reaction serves as the nucleus, enabling a good foam to be obtained. However, the above reaction inhibitor also acts to inhibit such initial foaming, preventing a good foam from being obtained. In addition, in cases where such compositions are used as millable addition-curable materials, when curing is carried out at a high speed so as to mold electrical wire, tubing or the like, a number of problems arise; for example, the surface remains tacky and a molded product having a smooth surface cannot be obtained.
Methods that have been proposed for increasing the heat resistance of silicone compositions include the approach of adding a heat resistance-imparting agent. Heat resistance-imparting agents that have been mentioned include amine compounds such as hindered amines (Patent Document 8: JP-A 2004-190013). However, amine compounds act as catalyst poisons in hydrosilylation reactions, and thus are undesirable. In particular, they cannot be used for molding in a short period of time.
A method for increasing the heat resistance of silicone compositions by adding a metal oxide such as iron oxide, titanium oxide, cerium oxide, magnesium oxide, aluminum oxide or zinc oxide has also been disclosed (Patent Document 9: JP-A 2006-225420). However, the addition of these metal oxides greatly lowers the transparency of the composition, and so this approach cannot be applied to materials required to have transparency.